What rule did Odysseus break?

Odysseus broke the rule of hubris, or excessive pride, when he revealed his identity to the Cyclops Polyphemus after blinding him. This act of boasting led to Polyphemus cursing him, which ultimately prolonged his journey home to Ithaca and brought further misfortune upon him and his crew. His failure to heed the advice of the gods and remain humble resulted in dire consequences throughout his odyssey.